Mosquitoes are a family of small, midge-like flies: the Culicidae. Although a few species are harmless or even useful to humanity, the females of most species are ectoparasites whose tube-like mouthparts (called a proboscis) pierce the hosts' skin to suck the blood. The word "mosquito" (formed by mosca and diminutive ito) is from the Spanish or Portuguese for "little fly". Thousands of species feed on the blood of various kinds of hosts, mainly vertebrates, including mammals, birds, reptiles, amphibians, and even some kinds of fish. Some mosquitoes also attack invertebrates, mainly arthropods. Though the loss of blood is seldom of any importance to the victim, the saliva of the mosquito often causes an irritating rash that is a serious nuisance. Much more serious though, are the roles of many species of mosquitoes as vectors of diseases. In passing from host to host, some transmit extremely harmful infections such as malaria, yellow fever, west nile virus and filariasis.